The present invention relates to a new and distinct cultivar of Begonia, of the family Begoniaceae, and given the cultivar name, ‘Cool Breeze Pewter’. This plant originated from planned breeding program for a colorful series of landscape Begonia. The new cultivar originated from a cross between Begonia hemsleyana (unpatented), as the seed parent (unpatented), and Begonia U489 (unpatented), as the pollen parent. This selection is uniquely characterized by:                1. broad, palmately lobed leaves,        2. showy silvered leaves with green spot by the petiole,        3. red leaf backs,        4. a bushy habit, and        5. excellent vigor.        
Compared to the seed parent Begonia hemsleyana, an unpatented plant, the new cultivar has leaves palmately lobed rather than palmately compound and heavily silvered rather than silver spotted.
Compared to the pollen parent, Begonia U489, an unpatented plant, the new cultivar is broader in habit, better branched, and with leaves that lobed rather than entire.
Compared to Begonia ‘Metallic Mist’, U.S. Plant Pat. No. 19,567, the new cultivar is larger and bushier, with larger, flatter leaves that have a green spot near the petiole rather than dark veins with silver.
Compared to Begonia ‘Cool Breeze Rouge’, U.S. application Ser. No. 13/986,388, the new cultivar stays all silver rather than getting a rose blush in cool temperatures.
Compared to Begonia ‘Cool Breeze Glacier’, U.S. application Ser. No. 13/987,232, the new cultivar has leaves that are pewter in color (on topside) rather than having interveinal silvering.
The new variety has been reproduced only by asexual propagation (leaf cuttings and tissue culture). Each of the progeny exhibits identical characteristics to the original plant. Asexual propagation by micropropagation as done in Canby, Oreg., shows that the foregoing characteristics and distinctions come true to form and are established and transmitted through succeeding propagations. The present invention has not been evaluated under all possible environmental conditions. The phenotype may vary with variations in environment without a change in the genotype of the plant.